1. Field of the Invention
This invention relates generally to data acquisition circuitry and, in particular, to multichannel data acquisition circuitry for use with arrays of hydrophones.
2. Description of the Prior Art
FIG. 1 is a block diagram of a portion of a data acquisition system of a type referred to as a Second-Stage Signal Processing Subsystem, which constitutes prior art relative to which the present invention is an improvement. A First-Stage Signal Processing Subsystem (referred to in FIG. 1 by a reference numeral employed as input signal labels, but depicted as a structural element in later discussed FIG. 2A) receives hydrophone signals that are routed to First-Stage Signal Processing Subsystem Processors. Each Analog Processor channel provides two output signals, a tracking-validation (T-V) signal 3 and a LOG AMP signal 5, which are inputs to the Second-Stage Signal Processing Subsystem. The T-V signal 3 is a digital pulse having a leading edge that occurs approximately coincidentally with a peak of a received hydrophone signal. The duration of the T-V pulse 3 is determined by the width of the received hydrophone signal. Stated another way, T-V pulse 3 is derived from changes of energy state of the analog signal. The LOG AMP signal 5 has an amplitude that varies as a function of the incoming signal level, or other state, of the incoming signal. During the time the T-V pulse 3 is on, the LOG AMP signal 5 is constant. The two output signals 3 and 5 from the First Signal Processor thus provide a basis for establishing the time of arrival of a target hydrophone pulse, the duration of the pulse, and the pulse amplitude. The same formats of T-V signal 3 and LOG AMP signal 5 exist with respect to the present invention.
The prior art Second-Stage Signal Processing Subsystem accepts the T-V Signal 3 and LOG AMP signal 5 and provides digital outputs which are sent to a range computer (not shown). Two types of data are transmitted: lead words and data words. Timing information is obtained from a range time code generator. During normal operation, a lead word is generated every eight seconds and timing information (hours, minutes and seconds) 7 is stored in a lead word register 35. The lead word also contains site identification information 9, a bit which identifies the word as a lead word, and a special event code 11. The special event code 11 is entered by an operator using switches provided with the Second-Stage Signal Processing Subsystem.
Data words are generated whenever valid hydrophone signals are received (i.e, time coordinated with the asynchronous hydrophone outputs). The prior art Second-Stage Signal Processing Subsystem can be programmed to verify long, short or zero pulses, and also to reject pulses which are excessively long. Timing information for the data word 13 is obtained from a binary counter. The binary counter is reset at the same instant that the lead word is formed, and counts with a resolution of 10 microseconds until the next reset occurs (which will always be eight seconds later). When the T-V pulse 3 is received, timing information 13 is stored in the data word. The width of the T-V pulse 3 is determined and, if it is found to be a valid signal, it is classified as a frame, or ordinary pulse. The pulse width and pulse amplitude 15 data are stored in the data word, along with an identification 17 as to site, target and receiving hydrophone. In addition, a computer tag code is entered in the data word. Also, both the lead words and data words contain dummy bits having a fixed, predetermined pattern for identifying the beginning of the word.
After the data has been established, the lead words and data words are stored in a buffer 19. Buffer 19 provides temporary storage for these words until a communication link 21 is able to transfer them to the range computer (not shown) for further processing.
The prior art Second-Stage Signal Processing Subsystem includes seven data channels 23 for each target it is capable of tracking, only two of which are shown. Each data channel 23 in the prior art Second-Stage Signal Processing Subsystem is coupled to an analog processor channel in the First-Stage Signal Processing Subsystem 1 so as to receive the T-V signals 3 and the LOG AMP signals 5 that are generated as outputs of the mating analog processor channel.
Each Data Channel 23 is comprised of three basic components:
(1) a Digital Signal Verifier 25, PA0 (2) a Voltage-to-Frequency Converter 27, and PA0 (3) the Data word Register 29.
The Digital Signal Verifier 25 verifies each T-V signal 3 received on the basis of pulse width. Only signals conforming to the width requirements for a valid signal are verified. Front panel control switches enable some variation of the pulse width requirements. The Voltage-to-Frequency Converter 27 converts the LOG AMP signal 5 into a proportionate frequency representation. The Data Word Register 29 counts this frequency over an established time base to produce a binary representation of the pulse amplitude. The Data Word Register 29, provided in each data channel 23, temporarily stores the time of arrival of the leading edge of each T-V signal 3 that is verified by the Digital Signal Verifier 25. The Data Word Register 29 also determines and stores the amplitude and width of the T-V signal 3, and categorizes the signal, on the basis of pulse width, as either a Frame or Ordinary T-V signal. Complete identification of the T-V signal 3 is also a function of the Data Word Register 29. This identification consists of the target which generated the original signal, and the identification of the hydrophone and site which received the signal. The data temporarily stored in a particular Data Word Register 29 enables the generation of a Data Readout Request signal which identifies the associated Data Word Register 29 as one containing information to be conveyed to the range computer.
An electronic sensor 31 sequentially interrogates each data channel 23 to determine if its Data Readout Request signal is active. When the electronic scanner 31 locates such a data channel 23, it stops scanning until the stored data is transferred to the buffer 19. In the process of transferring the data to the buffer 19, a beginning-of-word code is added to the word format. The beginning-of-word code enables the range computer to define the beginning and end of a word, as it is being received.
After the data word is stored in the buffer 19, a Data Readout Acknowledge signal 33 is generated which frees the Digital Signal Verifier 25 and Data Word Register 29 to accept subsequent T-V signals 3, and to restart the scanner 31 on the sequential interrogation of data channels 23.
The timing information 13 stored in each Data Word Register 29 is an interpolation of a time from a last synchronizing signal 37 to the time that the leading edge of the T-V signal 3 is received. Therefore, so as to provide complete information on the timing of the T-V signal 3, the time at which the synchronizing signal 37 was received is also recorded. This is accomplished by the Lead Word Register 35, which operates similarly to a Data Word Register 29, differing only in the type of information it stores.
The buffer 19 provides a buffering function between the irregular rate of data output from the data channels 23 and the established data rate of the communication channel 21 that links the equipment at each site to the range computer. The output of the Second-Stage Signal Processing Subsystem is a signal wire which conveys the data in bit serial form to the communication link 21.
The prior art Second-Stage Signal Processing Subsystem also contains hydrophone switching control equipment (not shown) for switching the inputs to the analog processor channels to appropriate hydrophones, on the basis of received switching command codes. These switching command codes may be generated remotely by a utilization processor which finally utilizes the data. Typically such a utilization processor is a range computer, which is operable for commanding the switching at all sites. Alternatively the command codes may be generated locally by the operator at each site. Each switching command code is addressed to the seven analog processor channels of the Second-Stage Signal Processing Subsystem that are provided to track one particular target. The switching code keeps these channels connected to an array of seven hydrophones whose location within a hydrophone field provides optimum coverage of a particular target. The switching equipment also provides the encoding required to provide identification of the hydrophone from which a verified signal is received. This identification becomes part of the data word, as previously described.
One disadvantage of this prior art Second-Stage Signal Processing Subsystem is that only one output buffer (buffer 19) is available. Thus, if buffer 19 malfunctions, all data can be lost and the entire system disabled. A further disadvantage is that the Signal Verifier and Data Word Register are capable of accepting only one signal at a time from the array of hydrophones. As a result, if the Signal Verifier and Data Word Register are in use, other information being transmitted for that channel can be lost.
Some data acquisition systems of the prior art are illustrated in the following U.S. Patents.
U.S. Pat. No. 4,718,004 to Dalal discloses a sample data acquisition system. The data acquisition system includes a plurality of signal conditioners 14a, 14b, 14c and 14d, each for sampling a number of analog input signals. Each signal conditioner includes: an analog multiplexer (MUX) for sequentially sampling each of a plurality of analog input signals, an A/D converter for receiving an amplified version of a sampled analog signal and converting it to a 16 bit digital data word, and a microcomputer and memory for controlling data transfer and storing digital data words.
U.S. Pat. No. 4,980,870 to Spivey et al. discloses an array beamformer system including a plurality of acoustic detectors. Analog signals output from each detector are processed by separate converters, each converter comprising a low pass filter, an A/D converter, and a microprocessor. A multiplexer accumulates all signals for given times, and a high speed array processor performs recursive calculations to determine a signal vector.
U.S. Pat. No. 4,041,442 to Marquardt discloses an acoustic data acquisition system for acquiring acoustic information from an array and for transmitting the information through a single transmission line to remotely located data processing equipment. The array includes a plurality of sensors, a plurality of submultiplexers, a multiplexer and an A/D converter.
U.S. Pat. No. 5,033,034 to Paradise discloses an acoustic tracking system including a selected number of acoustic sensor elements, each having a separate signal conditioner coupled thereto. A processor receives conditioned signals from respective signal conditioners and enables comparisons of selected characteristics of received signals in order to determine a selected parameter related to the movement of a body.
U.S. Pat. No. 4,631,697 to Ferguson discloses a multichannel electronic waveform recorder for storing waveform data and time of occurrence information (i.e., a time-tag) for each stored value of an input waveform.
U.S. Pat. No. 4,638,445 to Mattaboni discloses a vision system for mobile robots that reads out arrays of sensors. A Decision Engine formulates a decision, a course of action, and determines a mode of operation for the robot.
U.S. Pat. No. 4,027,289 to Toman discloses a data measurement subsystem and provides for a plurality of navigational signal transmitters. Different subsystems include microprocessors and a data store. Interconnections are provided to a remote control.
U.S. Pat. No. 5,072,420 issued to Conley discloses an arbiter state machine. When data transfer for or from a FIFO nears an overrun or underrun condition, the data channel issues an urgent request to the arbiter state machine.
U.S. Pat. No. 4,809,217 issued to Floro discloses a periodic execution of an I/O scan sequence in which remote modules are addressed in sequence.